Prostaglandins (hereinafter referred to as PGs) is the name of the group of fatty acids which possess various physiological activities and are contained in human and animal tissues and organs. PGs basically contain the prostanoic acid skeleton of the following formula:
and some synthetic products may contain the above skeleton with some modification. PGs are classified into several types according to the structure and substituents on the five-membered ring, for example,
and the like. Further, they are classified into PG1s containing a 13,14-double bond; PG2s containing, 5,6- and 13,14-double bonds; and PG3s containing 5,6-, 13, 14- and 17,18-double bonds.
PGs are expressed as follows. In PGs, the carbons constituting an α-chain, an ω-chain and a five-membered ring are numbered according to the basic skeleton as follows:

That is, in the basic skeleton, the constituent carbon atoms are numbered in such a way that the carbon atom in the carboxyl group is C-1, and the α-chain contains C-2-C-7, the number increasing toward the ring, the five-membered ring contains C-8-C-12, and the ω-chain contains C-13-C-20. When the carbons of α-chain are fewer, the numbers of the carbon atoms ensuing C-2 should be properly shifted, and when more than 7, the compound is named provided that carbon at the C-2 position has substituent instead of carboxyl group (at the C-1 position). When the ω-chain contains fewer carbon atoms they should be numbered correspondingly smaller than 20, and when more than 8, the carbon atoms at the 21 position and thereafter should be regarded as a substituent. As configuration, it is considered according to that of the above essential skeleton unless otherwise described.
For example, PGD, PGE and PGF mean compounds having hydroxyl group at the C-9 and/or C-11 positions. In the present invention, PGs also include those having other group instead of the hydroxyl group on the C-9 and/or C-11 positions, they being named as 9-dehydroxy-9-substituted or 11-dehydroxy-11-substituted compounds.
In addition, PGs may include the isomers, such as bi-cyclic tautomers, optical isomers; geometrical isomers, or the like.
PGs are known to have various pharmacological and physiological activities, for example, vasodilation, inducing of inflammation, platelet aggregation, stimulating uterine muscle, stimulating intestinal muscle, anti-ulcer effect and the like. PGEs or PGFs are found to possess contraction of intestines caused by intestinal stimulation is great, while enteropooling effect is poor. Accordingly, it is impossible to use PGEs or PGFs as cathartics because of side effects such as stomachache caused by the intestinal contraction.
On the other hand, PGs having a 13,14-single bond and a C-15 constituting carbonyl group, and those having a 13,14-double bond and a C-15 constituting carbonyl group are found to exist in human or animal metabolites. These 13,14-dihydro-15-keto-prostaglandins and 15-keto-prostaglandins (hereinafter referred to as 15-keto-PGs) are known to be naturally produced metabolites by enzymatic metabolism of the corresponding PGs in vivo. These 15-keto-PGs have been reported to hardly exhibit various physiological activities that PGs possess and be pharmacologically and physiologically inactive metabolites [see, Acta Physiologica Scandinavica, 66, p. 509- (1966)].
U.S. Pat. No. 5,317,032 to Ueno et al. describes prostaglandin cathartics, including the existence of bi-cyclic tautomers. However, the pronounced activity as anti-constipation treatment and prevention agents of the bi-cyclic tautomers has not been heretofore known.
While estimating the pharmacological activities of the analogues of 15-keto-PGs, however, the present inventors have found that the corresponding bi-cyclic compounds, i.e., the bi-cyclic tautomers, substituted by one or more halogen atoms can be employed in small doses for relieving constipation. At the C-16 position, especially, fluorine atoms, can be employed in small doses for relieving constipation. Where desired, larger doses to cause strong cathartic effect can be employed, although the primary purpose of the present invention is to restore a normal number of bowel movements (3 to 7 per week).